The present invention relates to additive-containing resin molded articles which do not suffer from exudation or vaporization of the additive or reduction in molecular weight due to reaction between a polyester resin and the additive and to a process for producing the same.
Thermoplastic polyester resins are superior in strength and the like but inferior in weather resistance and stain resistance. In the manufacture of constructive materials and other molded articles by melt molding a polyester resin, additives such as an ultraviolet absorber and a stainproofing agent are mixed into the polyester resin to improve the weather resistance or stain resistance.
The problem of the resin molded articles having an additive physically incorporated therein as mentioned above is that the additive exudes on the surface and vaporizes with time so that weather resistance or stain resistance is not maintained over a long period of time.
To overcome this problem, polymerized ultraviolet absorbers, etc. that hardly vaporize have been developed. However, polymeric additives sometimes have poor compatibility with polyester resins or sometimes cause transparency reduction or coloration.
The present inventors had developed an additive-containing resin molded article obtained by incorporating a mono-functional additive having one functional group, such as a carboxyl group or a hydroxyl group, at the molecular terminal thereof into a polyester resin and allowing the additive to react with the polymer molecules to be bonded thereto. Because the additive is fixedly bonded to the polymer molecules, the additive-containing resin molded article is free from exudation or vaporization of the additive and therefore sustains the action of the additive for an extended period of time.
However, because the additive used in the above-described additive-containing resin molded article is mono-functional, when one molecule of the additive reacts with one polymer molecule of a polyester resin through, for example, an ester linkage, the polymer molecule is divided into a polymer molecule having the additive molecule bonded to one end thereof and a polymer molecule having no additive bonded.
It almost all molecules of a polyester resin and the additive molecules react to each other, the average molecular weight of the polyester resin is reduced approximately by half. As a result, the mechanical strength and other various physical properties of the resultant additive-containing resin molded article show considerable reductions. The reductions in physical properties due to molecular weight reduction cannot be negligible degree because they become conspicuous as the content or conversion of the reaction of the additive increases.
The present invention has been completed under the above circumstances. An object of the present invention is to provide an additive-containing resin molded article which suffers from little exudation or vaporization of the additive and retains the effect of the additive for a long period of time and also which has little reduction in various physical properties due to a reduction in molecular weight of a polyester resin and a process for producing the same.
The additive-containing resin molded article of the invention which accomplishes the above object is characterized in that a bi- or multi-functional additive having one or two or more of a functional hydroxyl group, carboxyl group, amino group, and ester bond is present in a molded article comprising a thermoplastic polyester resin in a bonded form to the polymer molecules of the polyester resin.
Because the additive is fixedly bonded to the polymer molecules, the additive-containing resin molded article is free from exudation or vaporization of the additive from the surface and therefore sustains the action of the additive for an extended period of time.
Because the additive is bi- or multi-functional, it is less causative of molecular weight reduction of the polyester resin. For example, as depicted as a conceptual scheme in FIG. 1, when a molecule M of a bi-functional additive reacts with two polymer molecules P, P of a polyester resin at the ester linkage, there are produced a polymer molecule P1 having therein the additive molecule M and two polymer molecules P2, P2 split by reaction. Therefore, even if the additive molecules react with almost all the polymer molecules of a polyester resin, a reduction in average molecular weight of the polyester resin is limited to about ⅔. Likewise, where tri-functional additive molecules react with almost all the polymer molecules of a polyester resin, the average molecular weight of the polyester resin is reduced only to about xc2xe. Thus the reduction in average molecular weight of a polyester resin caused by the reaction with a bi- or multi-functional additive is less than that caused by the reaction with a mono-functional additive, and resultant reductions in various physical properties are therefore suppressed.
The above-described additive-containing resin molded article can be produced by the production process of the present invention which is characterized in that when a thermoplastic polyester resin is melt-molded, a bi- or multi-functional additive having one or two or more of a functional hydroxyl group, carboxyl group, amino group, and ester bond is added and allowed to react with polymer molecules of the molten polyester resin. The reaction can be carried out by utilizing conventional methods.
The reaction types between the polymer molecules and the additive include alcoholysis (the reaction of additives having a hydroxyl group), acidolysis (the reaction of additives having a carboxyl group), aminolysis (the reaction of additives having an amino group), and transesterification (the reaction of additives having an ester bond). It is considered that the additive is fixed to the polymer molecule through an ester linkage in the case of acidolysis, alcoholysis or transesterification and through an amide linkage in the case of aminolysis.
When the additive bonds to polymer molecules in this way, the polymer molecules are cut to reduce its molecular weight, but since the additive is bi- or multi-functional as mentioned above, the molecular weight reduction is smaller than that caused by a mono-functional additive.
Another additive-containing resin molded article according to the present invention is characterized by being an integral laminate composed of an additive-containing layer wherein a bi- or multi-functional additive having one or two or more of a functional hydroxyl group, carboxyl group, amino group, and ester bond is present in a bonded form to the polymer molecules of a thermoplastic polyester resin, and a thermoplastic resin layer wherein the additive in the bonded form to the polymer molecules is not present.
The thermoplastic resin which can be used in the above-described thermoplastic resin layer is not particularly limited and includes not only the polyester resin described below but also a vinyl chloride resin, polypropylene, polyethylene, an acrylic resin, an ABS resin, and polystyrene. The thermoplastic resin layer can contain the above-described bi- or multi-functional additive as long as the additive is not bonded to the polymer molecules.
The above-described molded article is also free from exudation and vaporization of the additive and enjoys the effect of the additive for an extended period of time because the additive in the additive-containing layer is fixedly bonded to the polymer molecules. Further, as the thermoplastic resin layer does not need to contain the additive, the additive to be used can be saved. Furthermore, not only because the molecular weight reduction of the polyester resin in the additive-containing layer is suppressed but because the thermoplastic resin layer has undergone no molecular weight reduction which might have been caused it reacted with the additive, the reductions of the molded article as a whole in mechanical strength and other physical properties are extremely small.
The additive-containing resin molded article having such a laminate structure can be produced by another production process of the present invention which is characterized in that when a thermoplastic resin and a thermoplastic polyester resin are melted and co-extruded, the above-described bi- or multi-functional additive is added to the polyester resin and allowed to react with the polymer molecules of the molten polyester resin. The reaction types and the bonding types between the additive and polymer molecules are as described previously.